AQA · Chemistry · 8462
GCSE Chemistry (AQA): Moles & Mass
Topic 3 — Quantitative Chemistry. Generated from the caption track of Cognito's lesson video "GCSE Chemistry - Moles & Mass - Avogadro's Constant | Formula for Moles, Mass & Mr (2027/28 exams)"; each card deep-links to the moment in the video it came from. Lesson 3.03 of Cognito's AQA GCSE Combined Science (Trilogy) and Chemistry course (Higher tier), filed under AQA Chemistry 8462. Teaching by Cognito — https://cognitoedu.org/coursesubtopic/c2-gcse-aqa-h-c_3.03.
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One mole of a substance has a mass in grams numerically equal to its ?.
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relative formula mass
Why can balanced equation coefficients be read as mole ratios?
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They give the fixed proportions in which substances react, so doubling one species doubles all the others.
What is the value of Avogadro's constant?
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6.02 × 10²³ per mole.
What is the mass of one mole of carbon (Ar = 12)?
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12 g.
What quantity does the mole measure?
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The amount of a substance — just as metres measure distance and seconds measure time.
What is the equation for the number of moles in a sample?
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moles = mass ÷ Mr.
What mass of carbon is contained in 3 moles of CO₂?
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36 g — multiply the 3 moles by the Ar of carbon (12).
How many moles are in 42.5 g of ammonia, NH₃ (Mr = 17)?
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2.5 moles, since 42.5 ÷ 17 = 2.5.
In Mg + 2HCl → MgCl₂ + H₂, how many moles of HCl react with one mole of magnesium?
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2 moles of HCl.
What is the mass of 3 moles of carbon dioxide (Mr = 44)?
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132 g, from mass = moles × Mr = 3 × 44.
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